Answer

One reason why a region of the genome would be highly conserved is if it coded for the rRNA used to make ribosomes and the tRNAs which carry amino acids for protein synthesis. These are highly conserved but do not code for protein. Another reason could be that these are non-coding sequences, there is little evolutionary impetus for these sections to change over time or from species to related species.

Work Step by Step

The key here is to mentally review past chapters and try to think of genes or other DNA elements which are critical but do not code for protein. rRNA is an obvious option, and tRNAs would be another. Also consider non-essential sequences; If a sequence has no function, why would (or would not) it change?